Best Exterior Polyurethane – Full Buying Guide with Tutorial

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Do you have outdoor wooden surfaces that you would like to protect from the elements, people, and traffic? The answer to your problem is exterior polyurethane, as it provides the best formulation for exterior wooden surfaces. Polyurethane paint is very easy to apply so you can do the job yourself and end up with an amazing finish to your outdoor wooden surfaces. In this article, we will be guiding you through the process of applying polyurethane paint to your outdoor wooden surfaces as well as providing you with the best products on the market.

A Closer Look at Polyurethane

What is the best exterior clear coat for wood? Polyurethane is something you should consider in this case, but what is it? Well, polyurethane is basically a super-tough form of varnish that is formulated to form microscopic molecule chains of resin that join tightly together as the resin dries. This will result in a finish that is abrasion, solvent, water, and impact-resistant and is far superior to an ordinary varnish finish. Some formulations of polyurethanes contain oil that leaves your wood with a warm amber hue. So, if you want your wood to retain its light color, then we suggest you use water-based polyurethane.

Water-Based vs Oil-Based Polyurethane

There have been many laws passed restricting the use of VOC’s (Volatile Organic Compounds), which has encouraged manufacturers to design alternatives to oil-based polyurethane. You need to seriously consider these alternatives before you purchase your polyurethane.

Water-Based or Oil-Modified Polyurethane

In the can, it looks slightly cloudy but when it dries, it produces an amber color that is tough similar to oil-based polyurethane. This type of polyurethane dries fast and can be applied to any type of wood. Cleaning is also easy using ordinary water. The VOC level of this type of polyurethane is the same as water-based poly.

Oil-Based Polyurethane

When dried it gives your wood a slight amber color that brings warmth to your wood surface. The finish is tough and durable, which can be attained by applying only two or three coats. The drying time for oil-based polyurethane is much longer than water-based poly, which means you need to wait longer before applying the next coat. The level of VOCs (Volatile Organic Compounds) is much higher than water-based polyurethane and, therefore, needs to be applied in well-ventilated areas and using protective equipment. Mineral spirits is needed to clean up afterward.

Water-Based Polyurethane

In the can, it has the appearance of milk but once dried is crystal clear. This is a good choice if you want to preserve the grain or color of your wood. It is a lot thinner than oil-based poly and so you need to apply more coats. You will find it dries very quickly and has a lower VOC (Volatile Organic Compound) level, but you still need to apply it in a well-ventilated area. Easily use soap and water to clean. Be very careful never to use ammonia-based cleaners on the dried polyurethane finish.

What is the Best Outdoor Polyurethane

Sometimes, you just need a little help in locating the right products, particularly if it the first time you are dealing with polyurethane. If this is the case, we recommend you do a little research before jumping into a project. To help you along, below are three recommendations of the best exterior polyurethane.

RUST-OLEUM: Ultimate Spar Urethane

What is the best exterior clear coat for wood? Like all other exterior polyurethane products, the formulation of RUST-Oleum Ultimate provides you with UV resistance. The sun’s UV rays cause damage to your wooden surfaces, which can result in discoloration. When you use this product, you can be sure that the sun’s rays will not damage your wooden surfaces at all.

Another advantage of this product is that once the polyurethane dries, it can withstand any rough activities as well as extreme weather conditions. The product also provides resistance against mildew and mold. Due to its oil-based formulation, it is water and moisture-resistant.

Even with all these amazing features, RUST-OLEUM Ultimate has some shortcomings. Over time it may lose its crystal-clear finish and start to yellow. The product also takes much longer to dry than many other similar products.

RUST-OLEUM Ultimate Spar Urethane

• A durable, protective poly finish for outdoor wood surfaces
• Oil-based formula for maximum durability
• UV-resistant with a rich, golden gloss finish

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ZAR Exterior Oil-Based Polyurethane

The ZAR Exterior Oil-based Polyurethane when applied, gives you a satin finish with a slight tint. This product brings out all the natural colors of your wood surface. So, you have both protection and a beautiful wood surface. It leaves you with the best high-gloss finish of any polyurethane product on the market today, much better than any water-based polyurethane can provide.

This product will give you the best modern finish with a touch of class. Other features include a tough durable finish once dried and UV resistance. There are also certain antioxidants present that assist in preventing discoloration.

ZAR Ultra Fast Drying Exterior Polyurethane

• Superior protection from weather and UV rays
• Dries to a premium satin finish
• Self-leveling formula for easy application

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Minwax Helmsman Indoor/Outdoor Spar Urethane

Minwax Helmsman is an excellent choice when you are encountering severe weather conditions. This product is also UV resistant, which prevents yellowing of the wood surface, and also prevents the wood from peeling. You will find it is fast drying, within 2 hours and cures leaving you with a crystal clear and shiny finish. However, the fast-drying time may not be an advantage, especially if you are working on a large project. Painting with a brush when the surface has already begun to dry will lead to major problems. The surface might then require sanding. Another problem is that the product is fairly thin and, therefore, soaks into the wood requiring you to apply more coats.

MINWAX Helmsman Indoor/Outdoor Spar Urethane

• Provides protection against sunlight, rain, and moisture
• Dries to a crystal clear semi-gloss finish
• Stays strong in changing temperatures

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Buying Guidelines for Outdoor Polyurethane

There are many things for you to consider before you go out and buy your polyurethane paint. We all want to protect our wood surfaces the best way we can, but the finish is also important. There is nothing more frustrating than after you have spent time and money to make your wood beautiful, you only land up being disappointed with the final result. Here are some things we found that you might need to think through before you purchase your polyurethane paint to avoid any frustrations.

Drying Time

When applying polyurethane products to your wooden surfaces, the drying time is a vital aspect you need to consider. If your particular project needs to be completed within a certain time, then we suggest you buy a fast drying polyurethane product.

Ultraviolet Resistance

A painted wooden surface is more durable than a surface with a clear finish when it comes to UV protection, as the clear finish product still allows damaging UV rays to shine through. Many add finely ground metallic compounds to their formulations for added UV resistance. However, none of these additives make it 100% effective. Also, by adding more of these additives, you will eventually make the product opaque.

Flexibility

With the constant change in temperature, humidity, and wind, your wood automatically expands and contracts. This means that your external polyurethane needs to have the correct mixture of oils and resins, this will allow it to flex together with the wood surface. Even though these additives are there to enhance your wood, many manufacturers recommend that you recoat your wood surface every year.  So, if your wood surface is still in excellent condition and needs another coat, all you need to do is remove any grease or oil stains and wipe the surface clean using mineral spirits before applying.

Easy to Use

Most people prefer to choose products that are effortless and simple to use, especially if you are just starting out. So, by buying polyurethane products that are easy to apply you can save time and money. You do not have to hire a professional to help you with your project, you can do it yourself.

Durability

This is one of the most important aspects for you to consider, as products that last long can protect your wood surface far better. When you buy long-lasting or durable products, it will save you a lot of money in repairs, as well as time saved in applying these durable products.

Applying Polyurethane Finish

Polyurethane is one of the easiest products to apply and is one of the most durable protective finishes for your wood surface. It comes in an oil or water-based formulation and can be applied using a brush, spray, or can be wiped on. No matter how you apply the polyurethane finish, you can be sure that you will see many good years of use.

Wood Preparation

Preparing your wood and providing a clean and smooth surface is vital for all wood finishes. However, it is even more crucial for a crystal-clear finish like polyurethane. Begin by using 220-grit sandpaper on the surface. If you have an open grain wood such as ash, walnut, or oak then you need to use wood grain filler before you apply the polyurethane, as this will form a smooth wood surface.

Next, you need to clean the wood surface making sure you remove all the sanding dust, by using a tack cloth and vacuum cleaner. You can also make use of a cloth soaked in mineral spirits if you are going to use oil-based polyurethane, or cheesecloth soaked in denatured alcohol if you are going to use water-based polyurethane.

How to Apply Oil-Based Polyurethane

You can thin your oil-based polyurethane by using mineral spirits, but most of the time this is not necessary. Make sure to read the manufactures instructions for clarity in this regard. Thinning your finish may help cause less of a build-up in the nooks and crannies of your wood surface.

To apply this type of polyurethane you can use a fine-bristle brush or a foam paintbrush. Try to avoid using cheap paintbrushes, as they tend to leave brush marks on the surface. The foam paintbrush is cheap, disposable, and very efficient for painting on flat surfaces. A bristled paintbrush is more effective for fine detail or molded edges.

When using a paintbrush ensure the brush strokes are always parallel to the wood grain. Try to complete each area using straight, long strokes with the brush to avoid making excessive air bubbles. The few air bubbles that do appear will disappear within seconds. Avoid making the finish coat too thick.

Once you have applied the first coat and it has dried completely, according to the manufacturer’s instructions, sand the surface lightly using 320-grit sandpaper, again always with the wood grain. When sanding, be careful not to sand too much of the polyurethane off, as this can result in damaging the wood surface underneath. Again make sure all sanding dust has been removed using a tack cloth and vacuum cleaner. The second coat can now be applied.

You can now duplicate the process until you are happy with the thickness and finish of the polyurethane coating. To protect your wood, two coats should be sufficient, however, where you experience a lot of moisture and wear and tear you will need to apply at least three coats. After each coat, you will notice that the finish is smoother. After the final coat, you need to use some fine grade steel wool until you have the right sheen, and then apply paste wax to complete the process.

How to Apply Water-Based Polyurethane

Oil stains and water-based polyurethane are not compatible. This means that if you are going to apply your water-based polyurethane over an oil stain you need to use some synthetic steel wool to make that area rougher. As water and oil do not mix, this will help to prevent the polyurethane from beading, much like water on top of the wax layer on your car.

Applying water-based polyurethane is very similar to that of oil-based polyurethane. Use a fine paintbrush, cloth, or foam pad to apply a thin layer of your polyurethane. Always remember to paint with the wood grain and avoid applying too much finish, which can result in the wood grain rising.

The first coat of water-based polyurethane should dry within two hours and then you can apply the second coat. With this process, you will not have to sand between coats, as you did with the oil-based polyurethane, but you need to read the manufacturer’s instructions first. When using water-based polyurethane you will have to apply at least three coats for your projects. On floors, you will need to apply a minimum of four coats to get the desired protection.

How to Wipe-On and Spray Polyurethane

The main advantage of using the wipe-on or spraying method of applying polyurethane is the thickness. Both of these methods can be used to apply very thin layers of finish in all those hard to reach places, but take care not to apply too much at one time. For the wipe-on method, use a dry, clean, lint-free cloth and for the spray method, it is the same as spray painting. Many users use the spray method for polyurethane when applying a topcoat, which will give you a beautiful smooth coat without any brush marks.

Frequently Asked Questions

Can You Apply Exterior Polyurethane?

Polyurethane gives you the best exterior finish on the market and is also exceptionally durable. However, you need to ensure that the polyurethane you buy has the correct ingredients with additives that will provide you with UV protection. The label on the container will indicate if it is for exterior use. This is vital, as wood will contract and expand outdoors and the polyurethane needs to flex with the wood.

Does Polyurethane Paint Make Your Wood Waterproof?

Polyurethane does not make your wood surface waterproof, but it does make it water-resistant. This finish will repel water and prevent it from being absorbed into the wood and does not make your wood surface 100% waterproof. Polyurethane gives your hardwood the needed protection.

Can You Apply Water-Based Polyurethane Over an Oil-Based Surface?

Yes, you can but you need to first prepare the wood surface properly before you apply the finish. this is not recommended though, and it would be best to match the different bases with each other.

Must Your Wood Surface be Sealed Before You Apply Polyurethane?

Most polyurethane does not require the wood to be sealed first, but if you are going to use a sealer ensure that the sealer and finish are compatible. Another alternative is to use a penetrating resin sealer which seals the wood completely. You can then also apply polyurethane over this finish to give you a smooth surface.

Is Polyurethane Toxic?

Yes, polyurethane contains isocyanates which is a toxic compound that scientists consider harmful to your lungs. Water-based versions are safer to use though. You can check the individual product guidelines for more information on this. Always wear protective gear though for best safety measures.

Can You Use Marine Polyurethane on Your Hardwood Floors?

Marine polyurethane is not necessarily the best product to use indoors. It has been specifically designed for outdoor use and withstanding harsh weather conditions. Rather find a specific interior polyurethane coating for this purpose.

The best exterior polyurethane finish will help to protect your wood against weather damage, while keeping it looking great. If you have outdoor furniture, decks or wooden finishes, then be sure to consider polyurethane for the perfect finish.